1. Field of the Invention
The present invention relates to a passive coherent location (xe2x80x9cPCLxe2x80x9d) radar system and method, and more particularly, to a system and method for measurement domain data association, also referred to as line tracking, for PCL radar applications.
2. Discussion of the Related Art
PCL radar systems may be represented by a multistatic radar system. A multistatic radar system has many receivers that are separated from one or more transmitters. The radiated signal from a transmitter arrives at a receiver via two separate paths. One path may be a direct path from the transmitter to the receiver, and the other path may be a target path that includes an indirect path from the transmitter to a target to the receiver. Measurements may include a total path length, or transit time, of the target path signal, the angle of arrival of the target path signal, and the frequency of the direct and target path signals. A difference in frequency may be detected according to a doppler effect if the target is in motion.
Knowledge of the transmitted signal is desirable at the receiver if information is to be extracted from the target path signal. The transmitted frequency is desired to determine the doppler frequency shift. A time or phase reference also is desired if the total scattered path length is to be determined. The frequency reference may be obtained from the direct signal. The time reference also may be obtained from the direct signal provided the distance between the transmitter and the receiver is known.
Multistatic radar systems may be capable of determining the presence of a target within the coverage of the radar, the location of the target position, and a velocity component, or doppler, relative to the radar. The process of locating the target position may include a measurement of a distance and the angle of arrival. The measurement determination of distance relative to the receiving site may require both the angle of arrival at the receiving site and the distance between transmitter and receiver. If the direct signal is available, it may be used as a reference signal to extract the doppler frequency shift.
In PCL radar systems, transmitters may be known as illuminators. Illuminators may be wideband sources of opportunities that include commercial frequency modulated (xe2x80x9cFMxe2x80x9d) broadcast transmitters and/or repeaters, commercial high-definition television (xe2x80x9cHDTVxe2x80x9d) broadcast transmitters and/or repeaters, and the like. Efficient techniques for wideband signal pre-detection processing and co-channel interference mitigation exist. Known approaches include an array of antennas used to receive the source of opportunity to be exploited, such as the primary illuminator, and any other co-channel signals present in the environment.
The different signals and their measurement data should be associated with the appropriate target. If the target association does not exist, then a new tracking may have to be implemented for the target. Conversely, old trackings should be eliminated from the system if updates are no longer being received. More efficient and expediant measurement data association may improve target tracking in PCL systems.
Accordingly, the present invention is directed to PCL applications and signal processing.
According to an embodiment, a method for associating a detection report having measurements to a line track is disclosed. The line track correlates to a signal reflected from a target detected by a passive coherent location system. The method comprises estimating a line track state vector from the measurements using a set of Kalman filters. The method also includes initializing the line track.
According to another embodiment, a method for associating measurement data to a line track correlating to a target is disclosed. A target signal is reflected from the target and is received by a passive coherent location system. The method includes determining a signal type for the signal. The method also includes converting the measurement data to filter data according to the signal type. The method also includes selecting a set of Kalman filters for the filter data according to the signal type. The method also includes propagating the line track. The method also includes identifying a detection report for the line track according to the measurement data. The method also includes computing measurement residuals and residual variances for the detection report according to the Kalman filters. The method also includes selecting the detection report for association with the line track according to the residuals.
According to an embodiment, a system for measurement data association of detection reports to a line track within a passive coherent location system is disclosed. The detection reports correlate to target signals received at the passive coherent location system. The system includes a state estimation means to associate new detection reports with existing line tracks and to estimate update states for extending line tracks. The system also includes a line track merge means to merge line tracks. The system also includes a line track termination means to terminate line tracks according to a specified criteria. The system also includes a line track initialization means to initiate new line tracks for unassociated detection reports.
According to another embodiment, a method for estimating line track states with detection association in a passive coherent location system is disclosed. The passive coherent location system receives target signals reflected from targets. The target signals have measurement valves. The method includes identifying a set of potential detection reports. The detection reports comprise measurement valves. The method also includes computing measurement residuals and residual variances for the measurement valves. The method also includes selecting candidate reports for line tracks from the set of potential detection reports according to the measurement residuals. The method also includes applying thresholds to the candidate detection reports. The method also includes associating the candidate detection reports passing the thresholds to the line tracks.
According to an embodiment, a method for associating new detection reports with existing line tracks in a passive coherent location system is disclosed. The method also includes gating a detection report-line track pair. The method also includes computing a score for the detection report-line track pair. The method also includes assigning a detection report of the detection report-line track pair to a line track of the detection report-line track pair according to the score.
According to an embodiment, a method for merging line tracks within a passive coherent location system is disclosed. The line tracks correlate to a target. The method also includes determining a list of line tracks and line track pairs. The method also includes calculating a measurement residual for each line track pair within the list. The method also includes determining merge criteria for the each line track pair. The method also includes comparing the measurement residual with gates correlating to the merge criteria. The method also includes removing a line track from the possible line track pair that satisfies the merge criteria.
According to an embodiment, a method for terminating a line track within a passive coherent location system is disclosed. The method also includes determining a termination criteria. The method also includes terminating the line track when the line track achieves the termination criteria.
According to an embodiment, a method for initializing new line tracks within a passive coherent location system is disclosed. The method also includes determining a configuration parameter for a new line track. The method also includes selecting an initialization process according to the configuration parameter. The method also includes performing the initialization process. The method also includes initializing a filter state of the new line track.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or maybe learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.